Vehicles are generally equipped with audio devices which play an audio sound inside a cabin. JP2776092B and JP1993-085288A disclose audio devices which perform localization of an audio sound so that person(s) on board is able to hear the audio sound from a given position in a cabin.
Incidentally, a vehicle driver is required to focus on driving (a traveling state of a vehicle which changes as the vehicle is driven) when enjoying driving a sports car, etc. Meanwhile, the driver tends to want to enjoy an audio sound for relaxation during steady travel.